Abstract
In cold forging processes, friction between materials and dies strongly influences material flow, forging load and damage to the
dies. Therefore, several methods to evaluate friction have been proposed. However those methods are not well simulated for the
severe conditions occurring in actual forging processes. In this study, a new method to evaluate friction coefficients is proposed.
The method applies backward extrusion, which enables us to create high pressure, large surface area expansion and a long
sliding distance, for the measurements. The unique feature of the die set used in this method is a rotating punch at a very slow
angular velocity. By a combination of measured load and torque, friction coefficients can be monitored throughout the
measurement process. Friction coefficients were measured for four types of lubrications; mineral oil, cold forging oil,
bonderizing and dry-in-place. With these results, the proposed method enables us to measure friction coefficients under severe
forming conditions.